Tissue engineering is increasingly useful as a therapeutic tool, particularly for treating skin wounds or vascular disease, and also as a tool for testing certain pharmaceuticals and cosmetics. For example, numerous skin substitute products are commercially available. Most of these products comprise a porous matrix of some type, often infiltrated with fibroblasts at the time of use, to function as a dermal layer and having keratinocytes or a thin epidermal autograft as an epidermal layer.
One such product is OrCel® (Ortec International, Inc.), a bilayer skin replacement having a collagen sponge that, upon use, contains allogenic dermal fibroblasts cultured on and within it as a dermal layer, and cultured allogenic keratinocytes on a non-porous side of the collagen sponge as an epidermal layer. Another bilayer skin replacement product, PermaDerm® (Cutanogen Corporation/Lonza, Walkersville, Inc.; Walkersville Md.), uses epidermal and dermal cells, preferably of autologous source, cultured on and within a collagen matrix. These exemplary products illustrate the vital role of cell culture in the preparation of such skin replacement products for therapeutic and/or research use.
Cell culture inserts comprising porous membranes, such as those sold by Nunc A/S (Roskilde, Denmark), are useful for studies of epithelial polarization, chemotaxis, macromolecule transport, and other applications. Generally, a porous membrane of either inorganic material, such as Anopore® (Anotec Separations Ltd.), or organic material, such as polycarbonate, serves as the growth and/or attachment surface for cultured cells, while the membrane is fixed to a rigid frame of culture-compatible material, such as polystyrene, that holds the membrane away from the bottom of the culture dish to allow culture media to reach both sides of the cells attached to and/or growing on the membrane.
To date, sponges, fabrics, membranes and other types of porous matrices for containing and supporting living cells, typically have been cultured in standard culture dishes, including those commonly referred to as bioassay dishes. Examples of bioassay dishes include Nunc® bioassay dishes, such as product numbers 240835 and 240845, and Corning® bioassay dishes, such as product numbers 431111 and 431301 (Corning Life Sciences, Acton Mass.). Bioassay dishes were initially designed for use with microbes, such as bacteria and yeasts, or non-anchorage dependent eukaryotic cells and are generally rigid transparent plastic dishes with a large surface area but having a low height so that multiple dishes may be stacked in an incubator.
Standard bioassay dishes have several drawbacks. Because skin replacement products require relatively large amounts of nutritive medium to progressively feed the growing structure, addition of medium is typically necessary. However, it is difficult to add culture medium to a standard bioassay dish without disrupting, displacing or otherwise damaging the cells in the dish. Moreover, the large volumes of media that must be contained in such dishes leads to excessive medium movement or sloshing when a bioassay dish must be moved or otherwise handled; this is undesirable due to the low profile or height of bioassay dishes.
There is thus a need for alternative culture dishes.